It means that the operating system told calibre that it could not create a folder on your device. Either the folder already exists and is set to read only, the device itself is write locked, or the device is full.

It means that the operating system told calibre that it could not create a folder on your device. Either the folder already exists and is set to read only, the device itself is write locked, or the device is full.

Device not full. How to find folder and change "read only"? Would device lock after some files were downloaded successfully? How to undo "write locked"?

After further thought, and noting that you are using linux, the problem could arise if you use both windows and linux. There might be a case difference in the folder name. Check if the folder "/media/usb1/database/media/books/Lawrenson, Brian" exists, but with different uppercase/lowercase letters.